Portable x-ray apparatus



April 21, 1970 c. E. VANDERPOOL 3,508,059

PORTABLE X-RAY APPARATUS 3 Sheets-Sheet 1 Filed March 10, 1966 INVENTOR CHARLES E. VANDER POOL BY slzgpzro and Ska silo ATTORNEYS April 21, 1970 c. E. VANDERPOOL PORTABLE X-RAY APPARATUS 5 Sheets-Sheet 3 Filed March 10, 1966 FIG. 5

INVENTOR CHARLES E. VANDERPOOL BY S/za oz'm Q/Ld Safu'ro ATTORNEYS April 21, 1970 c. E. VANDERPOOL 3,503,059

PORTABLE X-RAY APPARATUS Filed March 10, 1966 5 Sheets-Sheet s CHARLES E. VANDERPOOL BY Sfiapiro nd S/Iapiro ATTORNEY$ INVENTOR United States Patent 3,508,059 PORTABLE X-RAY APPARATUS Charles Enoch Vanderpool, 2827 Forest View Ave., Baltimore, Md. 21214 Filed Mar. 10, 1966, Ser. No. 533,281 Int. Cl. H01j 35/16 US. Cl. 250-90 6 Claims ABSTRACT OF THE DISCLOSURE Portable, low-powered X-ray generating apparatus includes a linear accelerator device having a series of drift tubes for accelerating an electron beam and directing it against an Xray target to cause the emanation of a narrow band of X-rays therefrom. The drift tubes are of increasing length along the beam, but the tube most adjacent to the target is relatively small and is located as close to the target as possible. A microwave oscillator provides a high frequency Wave which is coupled through a microwave amplifier and a coaxial transmission line to alternate ones of the drift tubes, the remaining drift tubes, including the last drift tube, being grounded. The sole source of energy is supplied by direct current batteries and a relatively low voltage of the order of hundreds of volts is supplied between the cathode of the linear accelerator device and the target. In one embodiment, the entire device is housed in a single housing with the linear accelerator contained within a shielding enclosure which consists of a pair of U-shaped lead channel members, the side walls of one of which is slipped between the side Walls of the other with the base portions opposing one another to form a rectangular shielding enclosure. In another embodiment, a main housing encloses the voltage supply, a timing circuit, the microwave oscillator, and the microwave amplifier, while a probe housing in the form of a lead shield around a linear accelerator tube is coupled to the main housing by means of a flexible, lowloss coaxial cable.

This invention relates to X-ray apparatus and more particularly to portable X-ray generating apparatus.

Conventional X-ray devices are widely used for diagnostic and therapeutic purposes. Such devices typically comprise an electron gun for directing an electron beam against an X-ray target and employ very high voltages of the order of thousands or tens of thousands of volts between the gun and target. The insulation requirements imposed by the use of voltages of this magnitude have inevitably resulted in very large and bulky structures Which, when considered with the requirement that devices of this character must be shielded, are far from portable. In addition, the photographs produced by such devices tend to be fuzzy and poorly defined, because the high voltages employed make it difficult to focus the electron beam sharply on the target.

While some prior art devices have employed linear accelerator means to impart very high energies to the beam to produce hard X-rays having energies of the order of millions of electron-volts, these devices have also employed very high voltages so as to obtain the highest energies possible and, accordingly, are faced with the same problems as to insulation, focusing, and Weight. More over, due to the very high energies employed, the shielding requirements become even more onerous and further reduce the portability of the devices.

There is, however, a need for a portable X-ray generating device. It would be convenient, for example, to employ such a device on emergency ambulances, in battle field situations, and aboard air and space craft.

Accordingly, it is the principal object of this invention to provide improved X-ray generating apparatus.

3,508,059 Patented Apr. 21, 1970 A more specific object is the provision of X-ray generating apparatus which is light in weight, compact and portable.

An additional object of the invention is the provision of an X-ray generating apparatus which provides a welldefined beam having X-rays confined to a narrow bandwidth.

A further object is the provision of X-ray generating apparatus which is powered solely by batteries.

Another object is the provision of X-ray generating apparatus employing a linear accelator device operating at a low voltage.

Yet another object is the provision of an embodiment of X-ray generating apparatus employing an improved shielding arrangement about a linear accelerator tube.

Still another object is the provision of X-ray generating apparatus having an auxiliary probe housing containing a shielded linear accelerator device.

Briefly, the invention contemplates the employment of a linear accelerator device including an X-ray target, a cathode providing a beam of electrons, and a series of drift tubes for accelerating the beam and directing it against the X-ray target to cause the emanation of a narrow band of X-rays therefrom. An important feature of the invention is the employment of a relatively low voltage of the order of hundreds of volts between the cathode and target. Although the drift tubes are of increasing length along the beam, the last tube is relatively small and is located as close tothe target as posible. This enables the beam to be focused to a very fine point on the target to produce an X-ray beam Which is well defined and which contains X-rays covering a narrow frequency band. A microwave oscillator provides a high frequency wave which is coupled through a microwave amplifier and a coaxial transmission line to alternate ones of the drift tubes, the remaining drift tubes, including the last drift tube, being grounded. The sole source of energy in the apparatus is supplied by direct current batteries, and a relay controls the application of voltage to the linear accelerator device, oscillator, and amplifier. The actuation of the relay is under the control of a timing switch circuit in the form of a one-shot multivibrator employing a pair of cross-coupled transistors and a uni-junction transistor. The actuation of a push switch causes the one-shot multivibrator to provide a pulse of current through the relay coil. At the end of a predetermined time interval, as governed by a timing control circuit, the unijunction transistor fires, blocking conduction through the coil.

According to one embodiment of the invention, the entire device is housed within a single housing. The linear accelerator tube is contained within a shielding enclosure which consists of a pair of 'U-shaped lead channel members the side walls of one of which is slipped between the side walls of the other with the base portions opposing one another to form a rectangular shielding enclosure about the linear accelerator tube. One of the base portions is provided with a window adjacent to the target to define the direction of emanation of the beam from the device.

In another embodiment of the invention, a main housing encloses the voltage supply, the timing circuit, the microwave oscillator, and the microwave amplifier, while a second probe housing, comprising a lead sheath about a linear accelerator tube, is coupled to the main housing by means of a low-loss coaxial cable for the microwave signal with the push switch for the timing circuit being connected at the end of a long, flexible cable.

These and other objects, features, and advantages of the invention and the manner in which the same are accomplished will become more readily apparent from a consideration of the following detailed description of the invention when taken in conjunction with the accompany- 9 ing drawings, Which illustrate preferred and exemplary embodiments, and wherein:

FIG. 1 is a circuit diagram of an X-ray generating device of the invention;

FIG. 2 is a schematic showing, partially broken away, of a linear accelerator tube of the invention;

FIG. 3 is a perspective view of the housing of a first embodiment of the invention, partially broken away to show the shielding enclosure surrounding the linear accelerator device;

FIG. 4 is an enlarged partial section view showing the linear accelerator device and shielding enclosure of FIG. 3; and

FIG. 5 is a perspective view of a second embodiment of the invention.

Turning to the circuit diagram of FIGURE 1, it will be seen that a device of the invention comprises, generally speaking, a linear accelerator device 10, a microwave generating device 12, a microwave amplifier 14, a timing circuit 16, and a pair of batteries 18 and 20.

The linear accelerator device is in the form of a linear accelerator tube and comprises an envelope 22, a cathode 24 heated by a filament 26, a series of drift tubes 28, 29, 30, 31, 32, 33, 34, 35, 36, and 37, and an X-ray target 38. Although the drift tubes are shown mounted within envelope 22, it is to be understood that they could be provided as coatings on the exterior surface of the envelope. When cathode 24 is heated by heater 26, it emits a beam of electrons which is projected axially of the drift tubes 28-37 until it impinges against the X-ray target 38. As will be explained more fully hereinafter, the drift tubes 2836 are of increasing length and are separated from each other by interaction gaps 40. The final drift tube 37 is relatively shorter, and a final interaction gap 41 separates drift tubes 36 and 37. The drift tubes serve as means for accelerating the beam of electrons to impart to it sufficient energy that X-rays are emitted from target 38 when the beam impinges thereagainst.

As will be explained more fully hereinafter, alternate drift tubes 28, 30, 32, 34, and 36 are energized by means of a microwave signal. This signal is generated by a microwave generator 12 in the form of a reflex klystron oscillator (a 2K25 reflex klystron may be employed) having a resonant cavity 42. A cathode 44 is heated by filament 46 and is located within a re-entrant portion 48 of the cavity. Likewise, a repeller electrode 50 is positioned within a second re-entrant portion 52 of the cavity. As is known in the art, grids 54 and 56 are provided, respectively, across the open ends of the re-entrant portions 48 and 52.

The microwave generator just described provides a microwave signal, which may be of the order of 10,000 megacycles. The signal is coupled by output coupling loop 58 through coaxial line 60 to a Waveguide 62. The waveguide is provided with a standing-wave ratio adjusting plunger 64 at one end thereof and with an output coupling loop 66 adjacent to its other end. The output coupling loop 66 is, in turn, coupled by means of a coaxial transmission line 68 to the microwave amplifier 14.

The microwave amplifier comprises two stages of amplification and employs tunnel diode amplifying devices. The first stage is coupled to coaxial line 68 and comprises a tunnel diode 70 in series with the line 68 and, on its output side, with an output resistor 72 and an adjustable output inductor 74 and thus, through a coaxial transmission line 76, to the primary winding 78 of a coupling transformer 80. The tunnel diode 70 is biased by the battery 20, which may comprise a six-volt battery, through a resistor 82 and choke coil 84. The second stage of amplification is coupled to the secondary winding 86 of transformer 80 through coaxial line 88 and comprises a tunnel diode 90, the output side of which is coupled through an output resistor 92, a variable inductor 94, and a coaxial line 96 to the primary winding 98 of a voltage step-up output transformer 100. This stage of amplifi- 4 cation is biased from battery 20 through resistor 102 and choke coil 104.

The secondary winding 102' of transformer is connected to a coaxial distribution line 104' by means of which the microwave signal is distributed through tap lines 106, 108, 110, 112, and 114 to drift tubes 36, 34, 32, 30 and 28, respectively. The alternate, odd-numbered drift tubes are connected to a ground line 116.

It will be understood that the linear accelerttor device 10 operates to increase the energy of the electron beam emitted by cathode 24 until it has sulficient energy to cause the emanation of X-rays from target 38. When the beam passes an interaction gap 40, the microwave signal causes the beam to accelerate. Since only those electrons which are in phase with the microwave signal at the interaction gap are so accelerated, it is necessary to make each of the drift tubes 2836 longer than the preceding one to compensate for the increasing speed of the beam in order to maintain the proper phase relationship between the beam and the microwave signal. Thus, the length of each of the drift tubes 28-36 is a function of the speed of the beam thereat and may be computed by techniques known in the linear accelerator art. In general, the length L of a drift tube will be governed by the equation:

where v is the particle velocity and f is the frequency of the microwave signal. The velocity v may, in turn be computed from Equation 6.39 appearing on page 10 5 of Vacuum Tubes by Karl Spalgenburg, 1948 edition, as follows:

where V is the voltage across the gaps. Reference may also be made to Livingston, High-Energy Accelerators, published by Interscience Publishers, Inc. N.Y., 1954, page 82, and Livingood, Principles of Cyclic Particle Accelerators, published by D. Van Nostrand Co. Inc. in 1961, pages 267-276. The width of the interaction gaps is not critical but must not be so close that an arc is created. However, it is important that the interaction gaps be of equal width.

Within each of the drift tubes the beam has a tendency to diverge as shown at in FIG. 2. The field provided by the microwave signal at the interaction gaps causes the beam to converge to a focus as shown at 122 in FIG. 2. In order to maintain the beam as fine as possible at its point of impingement against target 38, the final focus point 123 of the beam is made as close as possible to the target. This insures that only a minimum of divergence will occur between the focus point and the point of colli sion of the beam with the target. This is accomplished in the instant invention by positioning the relatively short final grounded drift tube 37 as close as possible to target 38 with the smallest possible interaction gap 41 between it and the preceding drift tube 36. This results in a beam which impinges against an area smaller than one square millimeter of the X-ray target 38, and a fine X-ray beam emanates from target 38. Due to the rather uniform energy of the electrons in the beam, the X-rays are restricted to a very narrow bandwidth. As a result, the apparatus of the invention makes it possible to take extremely sharp X-ray photographs despite the relatively low power of the X-rays.

Indeed, the low voltages employed contributes significantly to this result. Because only a few hundred volts of direct current are applied between the target 38 and the cathode 24, it is possible to make the interaction gap 41 and the spacing between drift tube 37 and target 38 quite small. Thus, since the final interaction gap 41 is closely adjacent to target 38, the divergence of the beam from interaction gap 41 to target 38 is minimal and the aforementioned clearly defined X-ray beam is emanated by target 38.

As previously mentioned, the sole sources of energy in the X-ray apparatus of the invention are the direct current batteries 18 and 20. Battery 18 may be a conventional 300 volt B battery, while battery 20 may be a 6.3 volt cell. As shown in FIG. 1, battery 18 has a positive side 130 and a negative side 132, which is connected through a voltage dropping resistor 134 to the repeller electrode 50 of the reflex klystron to provide 90 negative volts thereat. The cathode 44 of the reflex klystron oscillator is connected directly to the negative side 132 of the battery so that the necessary difierence in potential will be provided between cathode 44 and repeller electrode 50. The cathode 24 of the linear accelerator tube is also connected to the negative side 132 of battery 18. In order to connect positive terminal 130 of battery 18 to target 38, a switch 136 is provided. In addition, a switch 138 is connected between the positive side 130 of battery 18 and the grounded casing of reflex klystron 12 at 139. Both switch 136 and switch 138 are operated by a relay coil 140- in a manner to be explained more fully hereinafter and are shown ganged for this reason.

Filament 46 and filament 26 are connected across battery 20 through a switch 142. It will be noted that the negative side of battery 20 is connected to ground point 139. In order to indicate when switch 142 is closed and the aforesaid filaments are energized, an indicating lamp 144 is provided. In like manner, a neon indicating lamp 146 is connected between terminal 132 of battery 18 and switch 136 to indicate when switch 136' is closed and voltage from battery 18 is being applied to the X-ray target 38.

Switches 136 and 138 are controlled by relay 140 as previously mentioned. This relay is located within timing switch circuit 16. This circuit is a one-shot multivibrator of the type disclosed in the General Electric Transistor Manual, fifth edition, published in 1960 by the General Electric Company, pages 145 and 146, and comprises a first transistor 150, a second transistor 152, and a unijunction transistor 154. The collector electrode 156- of transistor 150 is coupled through parallel connected capacitor 158 and resistor 160 to the base electrode 162 of transistor 152. Similarly, collector 164 of transistor 152 is coupled through parallel connected capacitor 166 and resistor 168 to base electrode 170 of transistor 150. Base electrode 170 is connected through base resistor 172 to the left or positive terminal 130 of the battery 18, while base electrode 162 is connected through base resistor 174 to this terminal. The emitter electrode 176 of transistor 150 is connected to emitter electrode 178 of transistor 152 and through a common emitter resistor 180 and a resistor 182 to the terminal 130. The negative side 132 of the battery is connected through a voltage dropping resistor 184 and a push switch 186 to a junction 188, and suitable bias is provided to the collector electrodes 156 and 164 from junction 188 through collector resistors 190 and 192, respectively.

A timing control circuit is connected between collector electrode 156 of transistor 150 and the junction 189 between resistors 180 and 182 and comprises the relay coil 140, a resistor 194, an adjustable timing resistor 196 and a timing capacitor 198. The junction 199 between resistor 196 and capacitor 198 is coupled to the emitter electrode 200 of unijunction transistor 154. One base, electrode 202 of this transistor is coupled to the biasing junction 188, while the other base electrode 204 is connected through a resistor 206 to the emitter electrodes 176 and 178 of transistors 150 and 152, respectively.

The operation of the timing switch circuit 16 will be best explained by assuming that, at the outset, push switch 186 is open and the multivibrator circuit is in its quiescent state. The collector 156 will then be positive. When push switch 186 is closed a pulse of positive voltage will be applied to base electrode 170 of transistor 150 to trigger the circuit into conduction. This will cause a current to how from collector electrode 156 through the timing control circuit. This will energize relay coil 140, thus closing switches 136 and 138. The current will fiow through resistors 194 and 196 to charge timing capacitor 198. After a predetermined time interval as set by the selected value of adjustable timing resistor 196, the voltage charge built up across timing capacitor 198 will become sufiicient to cause unijunction transistor 154 to fire; and the multivibrator circuit will revert to its quiescent state. At this time, current will cease to flow through relay coil and switches 136 and 138 will revert to their Open condition. In this way, merely by depressing switch 186, the X-ray generating apparatus will become energized for a predetermined interval and produce a pulse of X-rays during this interval.

Turning now to FIG. 3, it will be seen that the device of the invention may be housed in a small, compact housing 210, having a carrying handle 212. The first panel of the housing may be hinged at 211 to provide access to the circuit components and may be latched closed by means of latches 213. The housing is provided with a window 214 to permit X-rays generated at target 38 to be directed upon the subject to be irradiated. Also seen on housing 210 is a timing adjusting knob 216 which is arranged to adjust adjustable timing resistor 196, a push button 218 arranged to operate push switch 186, and' a filament switch lever 220 adapted to operate filament switch 142. In addition, small transparent windows 222 and 224 are provided to expose indicating lamps 144 and 146. If desired, a meter 226 may be provided, the meter being connected at some suitable point in the circuit.

The linear accelerator device 10 is housed within a generally rectangular shielding enclosure made of lead sheets or of a fabric impregnated with lead. As shown more particularly in FIG. 4, the enclosure is constructed of a pair of generally U-shaped channel members 228 and 230. The channel member 228 has a base portion 232 and two side wall portions 234 and 236. Channel member 230 is similarly provided with a base portion 238 and two side wall portions 240 and 242. Member 230 is so dimensioned that its side wall portions 240 and 242 fit between the side wall portions 234 and 236 of member 228 with base portion 338 being opposed to base portion 232 to form a rectangular shielding enclosure about linear accelerator device 10. It will be understood that at the ends of this enclosure one of the members 228 and 230 is provided with end walls so that the linear accelerator device is completely shielded by the lead enclosure except at the portion of the enclosure corresponding to window 214. In FIG. 4, the target electrode 38 is shown in section with its tapered surface 244 facing toward the window 214 of housing 210. The base portion 238 of channel member 230 is provided with a corresponding window 246 so that X-rays emanating from surface 244 will be directed through windows 246 and 214.

It is to be understood that the embodiment depicted in FIGS. 3 and 4 is generally quite compact and may, for example, be eighteen inches in widh by five inches in height by two inches deep and weigh in the order of fifteen pounds. By replacing some of the components, such as the klystron oscillator with lighter components, the weight could be reduced. For example, if a tunnel diode microwave oscillator is employed, the device could weigh less than ten pounds. Moreover, if the power of the X-rays is kept low enough, the weight could be further reduced by employing brass shielding members in place of the lead members previously described.

The portability of an X-ray generating apparatus of the invention may be further enhanced by placing the linear accelerator device in a separate probe housing. This is shown in the embodiment of FIG. 5. Here, a main housing 250 is provided to house the batteries, the microwave generating device, the microwave amplifiers, the timing switch circuit, and the controls and indicating lamps with the exception of the control for push switch 186. The final microwave amplifier stage is coupled through a low-loss coaxial cable, such as RG/8U cable, to a remote probe housing 251 within which is located the linear accelerator device 10. The coaxial cable, voltage leads for the linear accelerator device, and a pair of wires to conduct filament current to the linear accelerator device are contained within a flexible cable 252. The probe housing 251 comprises a hollow cylindrical lead shield 254 having an enlarged head portion 255 which cylindrical head is provided with a suitable window 256 adjacent to the X-ray target. It is to be understood that the probe housing is insulated from the linear accelerator device by the use of a material such as silicone rubber to avoid a shock hazard. When the probe housing 251 is not in use, it may be secured to the main housing 250 by means of a pair of spring clips 258 and 260. In order to actuate the push switch 186 from a remote point a push button switch unit 262, including a push button 263, is provided and connected to the timing switch circuit 16 by means of a cable 264. When this cable is not in use, .it may be wound about a hook member 266 with a suitable spring clip 268 being provided to hold the switch unit 262.

As in the embodiment of FIG. 3, the main housing 250 is provided with a suitable carrying handle 270, a meter 272, a timing resistor control dial 274, and a filament switch 276. Windows 278 and 280 may be provided to expose indicating lamps 146 and 144, as in the embodiment of FIG. 3.

In use, the probe housing 251 and switch unit 262 may be carried some distance from the main housing 250. The window 256 is directed toward the body to be irradiated with X-rays, and the operator then depresses the push button 263 to energize the apparatus and cause the emanation of a pulse of X-rays for a predetermined time interval as previously explained.

While preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims. For example, other types of microwave oscillators, amplifiers, and timing circuits could be employed in the device. Accordingly, the foregoing embodiments are to be considered illustrative rather than restrictive of the invention, and those modifications which come within the meaning and range of equivalency of the claims are to be included therein.

The invention claimed is:

1. Portable X-ray apparatus for generating low power, high definition X-rays comprising: a linear accelerator device including an X-ray target, means providing a beam of electrons, and linear accelerator means for accelerating said beam and directing said beam as a fine point against said X-ray target to cause the emanation of a narrow band of X-rays therefrom, said linear accelerator means comprising a plurality of drift tubes surrounding said electron beam between said means providing a beam of electrons and said X-ray target, said drift tubes being dimensioned to impart acceleration to said beam; means providing a high frequency wave; means coupling said wave to alternate drift tubes, the remaining drift tubes being grounded; power supply means including a battery and providing a voltage having a magnitude in the order of hundreds of volts; and switch means for applying said voltage to said linear accelerator device between said target and said means providing a beam of electrons for a predetermined time interval, whereby a pulse of X-rays will emanate from said target.

2. X-ray apparatus as recited in t 'r m 1, wherein h energy of said X-rays falls within the range 30,000 electron-volts through 500,000 electron-volts.

3. X-ray apparatus as recited in claim 1, wherein the drift tube most adjacent to said target is grounded and positioned as close as possible to said target, whereby said beam is finely focused at its point of impingement against said target and a narrow band of X-rays will emanate therefrom in a finely defined beam.

4. X-ray apparatus as recited in claim 3, wherein said beam impinges against an area of said target not exceeding one square millimeter.

5. Portable X-ray apparatus for generating low power, high definition X-rays comprising: a linear accelerator device including an X-ray target, means providing a beam of electrons, and linear accelerator means for accelerating said beam and directing said beam as a fine point against said X-ray target to cause the elimination of a narrow band of X-rays therefrom; means providing a high frequency wave; means coupling said wave to said linear accelerator means; power supply means including a battery and providing a voltage having a magnitude in the order of hundreds of volts; switch means for applying said voltage to said linear accelerator device between said target and said means providing a beam of electrons for a predetermined time interval, whereby a pulse of X-rays will emanate from said target; and shield means enclosing said linear accelerator device, said shield means comprising a first U-shaped lead channel member having a base wall and a pair of side walls, a second U-shaped lead channel member having a base wall and a pair of side walls, the side walls of said first member being placed between the side walls of said second member with the base wall of said first member being opposed to the base wall of the second member to form a shielding enclosure about said linear accelerator device, one of said base walls being provided with a window adjacent to said X-ray target so that X-rays emanating from said target will leave said apparatus in a path as defined by said window.

6. In X-ray generating apparatus, an X-ray generating device and shield means enclosing said device, said shield means comprising a first U-shaped lead channel member having a base wall and a pair of side walls, a second U-shaped lead channel member having a base wall and a pair of side walls, the side walls of said first member being placed between the side walls of said second member with the base wall of said first member being opposed to the base wall of the second member to form a shielding enclosure about said device, one of said base walls being provided with a window so that X-rays emanating from said device will leave said apparatus in a path as defined by said window.

References Cited UNITED STATES PATENTS 1,870,959 8/1932 Morrison 250-91 2,543,082 2/1951 Webster 315-6 2,556,978 6/1951 Pierce 315-6 2,883,554 4/1959 Reed et al. 25095 2,909,664 10/ 1959 Zunick et al. 250 3,329,816 7/1967 Grundhauser et al. 25092 3,348,051 10/1967 Weighart et al. 250103 RALPH G. NILSON, Primary Examiner A. L. BIRCH, Assistant Examiner US. Cl. X.R.

UNITED sTATEs PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 508, 059 Dated April 21, 1970 Inventor(s) CHARLES ENOCH VANDERPOOL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 11, "accelator" should read --acce1era.tor--. Column 4, line 9, "accelerttor" should read --acce1erator Column 8, line 17, 'elirninaficion should read emanation SIGNED AND SEALED AUG 4 1970 (SEAL) mm I." my JR. Edward M- Ficwhfl', I Gamissioner of Patents Ameating Officer F ORM PO-IOSO (10-69) USCOMM-DC OOBTQ-PQD l 0.! GOVIINNI!" PIIIIIING OIHCI 1.. 0-866-334 

